Field of the Invention
The present invention relates to systems for drilling or servicing wellbores, more particularly, to a coiled tubing system for drilling or servicing wellbores by employing a rotary continuous pipe.
Description of the Related Art
Hydrocarbon fluids such as oil and natural gas are extracted from subterranean formations or reservoirs by drilling wells penetrating the reservoirs. Directional drilling using steering techniques can form deviated wellbores to reach reservoirs that are not located directly below a wellhead or a rig. A deviated wellbore is a wellbore that is intentionally drilled away from vertical. A deviated wellbore can include one or more inclined portions and one or more horizontal portions. A variety of drilling systems and techniques have been employed to provide control over the direction of drilling when preparing a wellbore or a series of wellbores having deviated sections.
Traditionally oil and gas wells have been drilled using a drill string formed by connected drill pipes with a drill bit included at the lower end of the drill string. Drill pipes are steel pipes having connectable end sections allowing them to join with other drill pipes to form the drill string. The drilling operation, which is often called rotary drilling, is performed by rotating the entire drill string and the connected drill bit from a rig on the earth surface. At the rig, conventionally, two different types of equipment, either a top drive or a rotary table drive, can be used for generating the needed rotational power to rotate the drill string. Alternatively, only the drill bit can be rotated by a down-hole motor attached to the lower end of the string. The motor typically has a rotor-stator to generate torque as a drilling fluid passes through the motor, a bent housing to deviate the hole by the required amount and a bit rotatably supported at the end for drilling the bore.
As the drilling operation advances into the earth, additional drill pipes are added to the drill string to drill deeper. However, an important drawback with this drilling technology is the significant time and energy lost caused by adding and removing new drill pipes.
Coiled tubing has been a useful apparatus in oil field drilling and related operations. Coiled tubing drilling does not use individual sections of drill pipe that are screwed together. Instead, a continuous length of metal tubing is fed off of a reel and sent down the wellbore. In a typical coiled tubing operation the metal tubing is unreeled from a tubing coil for either drilling a wellbore or providing a conduit within open or cased wellbores for workovers. The potential of coiled tubing to significantly reduce drilling costs with respect to conventional drilling using drill pipe sections has been long recognized. Some of the potential cost saving factors include the running speed of coiled tubing units and the reduced pipe handling time. Furthermore, the coiled tubing has a smaller diameter than traditional drill pipe, resulting in generating a smaller volume of cuttings. In addition to reducing waste volumes, the surface footprint is smaller, the noise level is lower, and air emissions are reduced. Since coiled tubing offers an uninterrupted operation, it can also reduce formation damages caused by interrupted mud circulations.
Despite the significant potential cost savings by drilling with coiled tubing, coiled tubing cannot be rotated and this limits applications of coiled tubing in drilling and workover operations. As mentioned above a conventional drill string is rotated from the surface but because the coiled tubing supplied from and a portion of the coiled tubing remains on the reel, the coiled tubing cannot be rotated.
From the foregoing, there is a need therefore for a novel multi-task rig which overcomes the many disadvantages of the continuous coiled tubing drilling and conventional jointed pipe drilling.